DESCRIPTION (Taken from the application): The goal of this project is to gain a solid understanding of how extracellular calcium regulates osteoblast cell proliferation at the molecular level by addressing specific questions in three key areas: cell surface calcium sensing, mechanism, extracellular calcium-activated mitogenic signal pathways, and extracellular calcium-activated gene transcription. To accomplish this, we propose to 1 ) determine the role of the CaR in calcium-stimulated osteoblast proliferation. We will verify the presence of the CaR in osteoblasts and if yes, determine if it is functionally important in mediating the mitogenic effects of extracellular calcium; 2) determine the role of PKC isoforms in calcium-stimulated osteoblast proliferation. We will determine if PKC is activated by extracellular calcium and if so, determine which of the PKC isoforms are activated and whether it is functionally important; 3) define the molecular basis of transcriptional regulation of the Fral gene by extracellular calcium. We will identify basal and calcium responsive elements in the Fral promoter. If successful, we will identify transcriptional factors interacting with these regulatory elements. We will also determine which intracellular signal pathways mediate the effects of extracellular calcium on transcriptional activation of the Fral gene. Successful completion of this study will help to establish the molecular mechanism of how extracellular calcium stimulates osteoblast proliferation and will shed light on the role of calcium in bone remodeling. The results of this study may also provide opportunities to develop therapeutic drugs for treatment of bone diseases such as osteoporosis.